This invention relates generally to camera focusing equipment and in particular to a camera having automated apparatus for moving a camera lens element to focus an image at the film plane.
Automatic lens focusing systems have been discussed and disclosed in the literature for several years. These systems generally have a continuously movable rotating motor, controlled by an electrical signal, with the motor mechanically coupled to move a lens element parallel to its axis to focus an image at the film plane of the camera. In prior art systems, a continuous feedback interaction is provided to generate for the camera electronic circuitry an electrical signal representing either the present position of the lens in its path of movement or the quality of the present focus of the image at the film plane. In this manner, further movement of the lens, including the direction of movement, is controlled by the electrical circuitry.
Even though often discussed in the literature, automatic focusing systems have not been entirely successful in still or movie cameras. Part of the reason may be that the feedback interaction undesirably introduces an added degree of complexity in the camera system. In addition, even though the electronics packages used in current camera equipment generally take advantage of recent technological innovations to reduce their physical size, similar technological advances have not been adapted to reduce the size of motor drives for automatic focusing mechanisms. The motor drives noted in the art have used a continuously movable motor, typically an analog-driven D.C. motor, which is mechanically coupled as by a worm drive to move the lens element to the focus position. The mechanical and electrical constraints heretofore placed on this kind of motor operation have retarded its miniaturization.
Needless to say, stepping motors--which are typically larger in size and weight than continuously movable analog motors and which are well known in non-camera applications where their size and bulk (for meeting required torque requirements) are acceptable--have not generally been used for focusing in photographic cameras. This is so even though they could be driven by digital circuitry. Stepping motors have apparently not generally been used because the increment of rotational movement is often large, and cumbersome gearing is required to reduce the step size for precision focusing. Further, stepping motors themselves generally are relatively large and thus not considered suitable for camera systems.
It is therefore an object of this invention to provide an automatically focusing camera system in which the focusing process can be carried out using incremental motion, while maintaining precision movement of the lens element.
Other objects of the invention are to provide an automatic lens focusing apparatus which meets the torque requirement of the mechanical lens system, which is simple to maintain and to operate, which is reliable, and which results in a moderate camera size.
Yet other objects of the invention include providing a system which does not require continuous feedback interaction from the apparatus during the focusing operation, and which can be driven by ditigal circuits.
It is also an object that the automatic focusing equipment provide precise lens movement and that it require minimal mechanical gearing and linkages.